1. Technical Field
This disclosure relates to achromatic electro-optical shutters, and more specifically, to achromatic electro-optical shutters using super-twist nematic (STN) liquid crystal (LC) cells.
2. Background
A plano-stereoscopic display is one which produces the depth sense, stereopsis, by presenting appropriate left and right planar images to each respective eye. For the observer to be able to fuse these two planar images into a single stereoscopic view, the image for one eye must be isolated from the other. If the left eye, for example, also sees all or a portion of the intensity of the right image, there will be a perceived doubling of the image or “ghosting.” Incomplete left and right channel isolation, or crosstalk, is of great concern to the designer of a stereoscopic system. Such crosstalk may be caused by poor contrast performance of a liquid crystal (LC) shutter.
LC shutters have been used for 3D applications for many years. Usually, bend mode LC shutters, called PI cells are used for such applications. Even though a suitably designed PI cell LC shutter provides a relatively fast response time, it typically requires a sophisticated drive waveform to convert splayed LC mode to bend mode for it to function adequately. Furthermore, PI cell LC shutters have an undesirable spotty appearance for several minutes after power-down, during the gradual transition back to splay state. As an alternative, Super-twist nematic (STN) liquid crystal (LC) cells may be used. Conventional STN LC shutter solutions are advantageous in that they do not require an initial waveform and they have a uniform neutral appearance after power-down. However, the disadvantages of conventional STN LC-based shutters are that they typically use a high voltage to provide a high-density off-state, have a narrow field of view (FoV), and a relatively slow response time.